Slot antennas typically comprise a slot cut into a metal sheet or printed circuit board. Since some modern communication devices are required to operate in multiple frequency bands, multi-band slot antennas have been developed for use in such devices.
For instance, Chang (U.S. Pat. No. 7,006,048) describes a dual-band slot antenna for satellite and/or RFID communication systems. The slot antenna comprises two interconnected L-shaped slot antenna structures, and a printed circuit feed line that is coupled to both of the L-shaped slot antenna structures. Sun (U.S. Pat. No. 6,677,909) describes dual-band slot antenna that comprises a pair of meandering slots, and a coaxial feed cable that is connected to the meandering slots.
Planar inverted-F antennas (PIFA) are becoming increasingly common in wireless handheld communication devices due to their reduced size in comparison to conventional microstrip antenna designs. Therefore, PIFA antennas have been developed which include multiple resonant sections, each having a respective resonant frequency. However, since conventional PIFA antennas have a very limited bandwidth, broadband technologies, such as parasitic elements and/or multi-layer structures, have been used to modify the conventional PIFA antenna for multi-band and broadband applications.
These approaches increase the size of the antenna, making the resulting designs unattractive for modern handheld communication devices. Also, the additional resonant branches introduced by these approaches make the operational frequencies of the antennas difficult to tune. Further, the additional branches can introduce significant electromagnetic compatibility (EMC) and electromagnetic interference (EMI) problems.